The present invention relates to a method for use in the hydraulic roll control system of a papermaking machine or the like, in which method oil is pumped from a supply tank to points of service, wherein the oil is pumped at least at one low pressure level such as is required for the lubrication of the roll bearings and/or drive gearbox and at least at one high pressure level such as is required for pressure-loaded zones of a roll and in which pressurized system the oil being pumped is filtered and if necessary cooled and in which system the return circulation of oil from the points of service is passed back to the supply tank.
The invention further relates to a multipressure hydraulic roll control system suited for use in a papermaking machine or the like, in which system the oil is arranged to be pumped from a supply tank to the points of service at least at one low pressure level such as is required for the lubrication of the roll bearings and/or drive gearbox and at least at one high pressure level such as is required for the pressure-loaded zones of a roll and in which multipressure system the oil being pumped is filtered and if necessary cooled prior to being passed to the points of service and in which system the return circulation of oil from the points of service is arranged to be passed back to the supply tank.
A plurality of functions are today implemented in papermaking mills with the help of hydraulics. One of the most important hydraulics applications herein is the crown compensation of rolls. Furthermore, e.g., the adoption of long-nip presses in fast-running papermaking machines and the growing favor of covered rolls needing improved cooling circulation has pushed hydraulic roll control systems to dimensions corresponding to those of circulating oil lubrication systems. When implemented using conventional constructions and components, the overall costs of circulating fluid systems have increased steeper than could be anticipated from a linear extrapolation of costs on the basis of nominal pumping capacity required. Another factor urging toward larger systems is the adoption of large-scale hydraulic power supply centers serving a plurality of rolls in common. On new papermaking lines, there may be a great number of crown-compensated rolls, whereby the present convention of providing each roll with a dedicated hydraulic control center is an expensive solution for the system manufacturer and, frequently, for the end user, too. Revamping a mill with larger hydraulic systems is often hampered by the problem of finding sufficient footprint for a single hydraulic fluid supply tank. Hence, a need exists to manage with smaller supply tanks and simultaneously develop the technology and manufacture of larger systems toward higher cost efficiency.
The inception of the method and system according to the invention builds on the state of the art that is first explained by making reference to FIG. 1 illustrating at a very schematic level the principles of a typical circulating oil lubrication system. In a system of the kind shown herein, the hydraulic oil is taken from a supply tank 50, wherefrom it is distributed by means of a hydraulic pump 51a to lubricated points. The system also includes a standby pump 51b and check valves 52 required thereto. From the pump 51a, the hydraulic oil is taken advantageously via a two-way valve 53 and further via filters 54 and a cooler 55 to the lubricated points along a feed line denoted by reference numeral 56. The system pressure is regulated with the help of a bypass flow controlled by means of a two-way valve 57 wherefrom the return flow is directed back to the supply tank 50 along a piping line 58. The return flow of oil from the system to the supply tank 50 takes place along a return line 59.
Another example of the state-of-the art systems is shown in FIG. 2 illustrating a typical hydraulic system of a roll equipped with spray piping. In the conventional system shown in this diagram, an oil tank 60 is divided into two parts, whereby the tank is comprised of a return oil chamber 60a and a suction chamber 60b. The main reason for this two-compartment division is that as the supply pressure to the valve manifold of controlled-crown rolls is generally about 85 bar typical, coolers used for cooling the oil cannot be mounted directly on the supply lines, because standard-type coolers are specified for a maximum working pressure of about 25 bar. Consequently, the oil is cooled in a separate filtering/cooling circuit into which the oil is passed by a hydraulic pump 61a. Next to the pump 61a, the circulating oil is passed in a conventional manner through a filter 62a. A standby pump is denoted by reference numeral 61b and at filter connected thereto by reference numeral 62b, while the check valves required are denoted by reference numerals 63. Next to these, the filtering/cooling circuit is provided with a cooler 64 after which the forward flow 66 to the spray piping is taken with the help of suitable arrangements from a manifold 65. The manifold 65 is further connected by a line 67 to the suction chamber 60b of the oil tank 60 so that the oil can be supplied from the return oil chamber 60a to the filtering/cooling circuit and exhausted therefrom back to the suction chamber 60b. The oil to be passed to a high-pressure circuit 74 connected to the control valve manifold of the roll is taken from the suction chamber 60b via a pump 71a and a filter block 73. In FIG. 2, a standby pump of this circuit is denoted by reference numeral 71b and the check valves by reference numeral 72. Respectively, the oil supplied to the roll bearings and the drive gearbox is passed by a pump 81 a via a filter block 83. In this circuit, a standby pump is denoted by reference numeral 81b and the check valves by reference numeral 82. A return flow pipe back to the oil tank 60 is denoted by reference numeral 68.
The return oil chamber 60a forms about 60% of the overall volume of the tank 60. The volume of the return oil chamber 60a is effectively utilized, e.g., for separating entrained air bubbles from the oil. The suction chamber 60b serves only partially as the active volume of the tank 60, whereby it makes the tank dimensions larger but also functions as an internal manifold of the tank 60. Because roll control systems frequently need a high cooling power, the flow rate pumped through the filter 62a, 62b of the filtering/cooling circuit must be equal to the maximum flow rate of oil to be pumped through the actuators. This means that the oil returning from the roll is filtered twice before it is resupplied to the system. Such an almost double-capacity filtering arrangement imposes substantial extra costs on both the system manufacturer as well as the end user operating the system.
Improvements to the conventional system shown in FIG. 2 have been sought, e.g., from stripping off unnecessary filtering capacity. Still adhering to the elucidation of the state of the art, said approach is depicted in FIG. 3 illustrating a system comprising a low-pressure circuit 104 and a high-pressure circuit 114, complemented with a cooling circuit in which oil is taken by a hydraulic pump 91 from the return oil chamber 90a of supply tank 90 and passed via a cooler 93 and a check valve 92 along a return flow line 94 back to the suction chamber 90b of the tank. This arrangement omits the filtering circulation of FIG. 2 and hence has only the cooling circuit. However, all oil being pumped to the roll is filtered immediately after pumps 101a, 101b, 111a and 111b. Of these, pumps 101b and 111b serve as standby pumps.
At large flow rates, the most advantageous technique of implementing run-time replacement of filters has constituted a parallel connection of multiple filters in which the filters can be replaced one at a time. In FIG. 3, the filter banks are denoted by reference numerals 103 and 113. The valves and check valves of the low-pressure and high-pressure circuits are denoted by reference numerals 102, 105, 106, 112, 115 and 116, respectively. As mentioned above, the supply tank 90 still incorporates a suction chamber 90b serving as an oil distribution manifold between the separate low-pressure and high-pressure circuits 104, 114. A return flow pipe of oil exhausted from the roll control system is denoted by reference numeral 118 in FIG. 3.
In the above-described systems representing the state of the art, a major problem arises from the large size of the oil supply tank required therein and the great number of components necessary to implement the desired functions. The high-pressure circuits of conventional systems need coolers as well filters that are extremely costly. In addition to cost and size factors, prior-art systems are also hampered by the complicated constructions of the oil system.
It is an object of the present invention to provide an entirely novel type of method suited for use in the hydraulic roll control system of a papermaking machine or the like. To reach this goal, the method according to the invention is principally characterized in that in the method the oil is pumped from a tank by means of a pump or pumps into a single low-pressure circuit wherefrom the supply lines to desired points of service are passed through stages serving to stepwise elevate the line pressure to a desired high-pressure level.
The delivery of the low-pressure primary circuit pump or pumps is advantageously adapted to meet the overall demand of oil flows delivered to the points of service.
It is another object of the invention to provide a novel type of multipressure hydraulic roll control system designed according to a new concept. This kind of multipressure hydraulic control system is principally characterized in that the multipressure system is implemented as a single low-pressure circuit and is provided with a distribution manifold or manifolds through which the oil flows are adapted to pass toward the points of service essentially at the working pressure level of the low-pressure circuit and/or at pressure levels higher than that of the primary circuit by virtue of stepwise elevating the line pressure to the desired higher level with the help of a high-pressure pump or pumps.
In a multipressure system, the delivery of the low-pressure pumps feeding the oil from the tank to the low-pressure primary circuit is advantageously adapted to meet the overall demand of oil flows delivered to the points of service.
The method and the multipressure hydraulic roll control system according to the invention gives a significant advantage over conventional arrangements. Firstly, the invention facilitates a simplified construction of the oil tank as the tank need not any more include a separate return oil chamber and a suction chamber. Hence, the outer dimensions as well as the overall volume of the tank can be made smaller without departing from the design rules of equal system capacity. Furthermore, the invention manages with simpler filtering equipment. By virtue of the method and system according to the invention, the cooling circuit is easier to control, because the temperature of the oil flowing to the field points of service remains more constant. The adoption of the invention eliminates pressure drop losses due to unnecessary pressure elevation, since the low-pressure flows can be taken from a low-pressure primary circuit while the high-pressure lines are connected to a high-pressure circuit, respectively. The location of pumps can be made with greater freedom and at a greater distance from the oil tank than in the prior art as the pressurized oil distribution manifold assures a sufficiently high suction head at the pump inlets. The invention is also superior to the prior art by permitting the use of a cylindrical tank if its manufacture is found more advantageous than making a cubic tank. The manufacture of the tank is easier as less nozzles are required thereon. Other benefits and specifications of the invention will be evident from the detailed description of the invention whereby reference will be made to the appended drawings marked FIGS. 4 and 5.